Patients who are forced to sit relatively immobile for long periods of time often experience decubitus ulcers (also known as pressure or bed sores) of the skin due to the concentrated pressures upon the patients' ischium, sacrum and coccyx areas. The latter two occur as a function of unsupported rearward tilt of the pelvis about the ischium causing slouching and thereby contact of the sacrum and coccyx with the seat and backrest. Once a sore occurs, the patient historically has not been able to resume sitting until the sore heals. Physical contact of any kind with the affected area results in pressure, heat, and humidity buildup which will result in further injury to the site, infection, and oftentimes death from ensuing infection.
Along with pressure, this tilting of the pelvis also changes the lumbo-sacral curve of the lower back such that lower back pain and poor posture often results. Devices designed to support the lower back often degrade the seating environment. They reduce lower limb support by reducing the effective depth of the seat bottom and either force the body to sit in positions which are unnatural or do not give adequate cushioning and support for proper posture and comfort.
U.S. Pat. No. 4,688,285 of Robert discloses a medical cushion for minimizing pressure areas on portions of human anatomy. However, the cushion of this patent does not control the tilt of the pelvis due to the location of its aperture, and is not designed to support the lower back.
U.S. Pat. No. 4,122,567 of Hanson discloses an articulated bed having a U-shaped cavity at one of its ends. There is no disclosure in Hanson of means for eliminating pressure while seated, and in so doing also controlling the tilt of the Pelvis thereby removing contact pressure on Sacrum and Coccyx.
U.S. Pat. No. 3,856,349 of Light discloses (at column 1) that ". . . during prolonged sitting the lower back, at rest, gradually assumes the curvature of the material it is resting against, and, if this is a cushion or a curved seat back, the person's natural lordosis is accentuated." However, the device of this patent does not provide adequate cushioning to the lower back and, furthermore, artificially constrains the back into an unnatural and uncomfortable position. It particularly does not eliminate contact pressure to the sacrum and coccyx.
U.S. Pat. No. 4,471,993 of Watson describes a device for supporting the lower back area of the body comprising a front resilient member and an inner core. However, because of the dimensions and configuration of the device of this patent, one using it is pushed forward in the seat and thus cannot utilize all of the support afforded by the entire length of the seat bottom.
U.S. Pat. No. 5,039,158 of Maier, describes a multi-segmented lumbo-sacral support which provides support to the curvature of the lower back while simultaneously alleviating local pressure on the bony protuberances of the spinal column. However, the device does not suspend the sacral area such that it remains contact free, and its support is limited to the lumbo-sacral curve of the lower back, and can be used only by patients with relatively unimpeded range of motion in their hips.
U.S. Pat. No. 4,951,334 of Maier, describes a pressure relief cushion designed to eliminate pressure on the Ischium and control pelvic tilt to minimize and often eliminate sacrum and coccyx pressure. The design by itself does not ensure that the sacrum and coccyx areas would remain contact free for all patients, particularly those with limited hip rotation, and provides no means for direct support of the lower back.